Electric blasting cap and ignition material for the same



E w E L A H ELECTRIC BLASTING CAP AND IGNITION MATERIAL FOR THE SAME Filed March 18, 1929 Patented Mar. 24, 1931 UNITED STATES PATENT OFFICE HAROLD A. LEWIS, OF WOODBURY, NEW JERSEY, ASSIGNOR TO E. I. DU PONT DE NEMOULS & COMPANY, OF WILMINGTON, DELAWARE, A CORPORATION OF DELA- WARE EIECTRIC B LASTING CAP AND IGNITION MATERIAL FOR THE SAME Application filed March 18, 1929.

This invention relates to electric blasting caps, and more particularly to an improved ignition mixture for the same, and consists essentially in the use of a mixture of a sulphocyanate, an oxidizing agent, and a low flash point fuel as an ignition material for the blasting caps.

Electric blasting caps, as commonly manufactured, comprise a metallic shell containing a pressed explosive charge and an igniter. In some cases the pressed explosive charge has been a single charge of a primary detonating compound such as mercury fulminate, or a mixture of this material with an oxidizing agent such as potassium chlorate; and in other cases it has consisted of two separate charges, one a base charge and the other a primer charge. Among the explosives used for the base charge have been, for example, trinitrotoluene, picric acid, tetranitromethylaniline (tetryl) tetranitropenterythrite, erythrol tetranitrate, nitrated ivory nut meal, and ground smokeless powder. For the priming charge there have been used primary detonating compounds, such as mercury fulminate, cyanurtriazide, and lead axide, various oxidizing agents such as potassium chlorate being often mixed with the priming compound, and various ignition and binding compounds such as lead tritroresorcinate being often mixed with or superimposed upon the more difiicultly ignitible primers such as lead azide. In some cases an inner capsule has been used with the primer charge in order to get additional confinement, and thereby increase the efiiciency of the detonator, while in other cases no such capsule has been employed.

For the ignition of these electric blasting caps two general methods have been in use; one, a so called match head in which a wire is surrounded by a mass or bulk of ignitible material; and, two, a bridge wire embedded in a loose charge of ignitible material. In both cases the ignition is afi'ected by heat gener- "ated in the bridge wire by passage of an. electric current from an outside sourcev through leading wires attached to said bridge. For the loose charge, to which the present invention relates, there have been Serial No. 347,915.

used, for example, mercury fulminate, either alone or with potassium chlorate, mixtures of mercury fulminate, antimony sulphide, potassium chlorate, and gun cotton. A mixture comprising eighty parts of mercury fulminate and twenty parts of potassium chlorate has been, in most common use.

These mixtures heretofore used are expensive because of the high proportion of costly mercury fulminate included; it has been found in the past impractical to reduce the cost materially by decreasing the proportion of fulminate because of erratic performance. In addition, the mercury fulminate cannot be used in certain metallic shells because the free mercury, almost invariably present as impurity in fulminate, caused oxidation of or an amalgamation with such metals; for example, mercury fulminate cannot be satisfactorily used in alumir'im shells, which shells have been almos1 universally employed with lead azide primed detonators. Also mixtures of mercury fulminate and potassium chlorate when used in contact with lead azide, have been generally considered responsible for spontaneous explosions and therefore incompatible. F urthermore, mercury fulminate and potassium chlorate mixtures are hydroscopic. In moist condition they exert a powerful corrosive action on certain metals and alloys whose other properties aresatisfactory for bridge wires; it has, therefore, been necessary in many cases to use expensive metals, such as platinum, for bridge wires in order to overcome this corrosion. Also, when moist, these mixtures frequently fail to ignite.

The object of my invention is to provide an ignition compound for electric blasting caps which is cheaper than those most C0111- monly used heretofore. A further object is to provide an ignition compound which may be used in any of the metals which have heretofore been used for the manufacture of blasting cap shells, and particularly one which may be used in the presence of lead azide. Further objects will be apparent as the description proceeds.

, These objects are accomplished by the following invention, in which I have found that an ignition com ound comprising a sulphocyanate, an oxi izing agent and a low ignition-point fuel produces most satisfactory results.

A suitable sulphocyanate for this purpose is lead sulphocyanate, although other sulphocyanates may be used, such, for example, as copper sulphocyanate. A suitable oxidizing material for use in my composition is potassium chlorate, although I may use other oxidizing agents, such as potassium perchlorate or barium nitrate. I have found that for a low ignition-point fuel nitrocellulose or pyro powder is very satisfactory, although any of the low ignition-point fuels, for instance, salts of various organic acids, such as the lead salts of styphnic acid or picric acid, may be used. I have found, however, that the nitric esters are particularly well suited to my purpose, because of their availability. Another example of low flash point nitric esters having satisfactory properties for my purpose is nitro-starch, tho-ugh this mate rial is less satisfactory than ground smoke less powder because of its tendency towards instability and ready moisture absorption.

By way of description, the following is given, but it is to be understood that this invention is not to be limited to the materials or proportions given below, and that this example is merely illustrative of one of the preferred embodiments of my invention suitable for the purpose described:

P r e nt Lead sulphocyanate till-b0 Potassium chlorate 10-30 Ground smokeless powder 3050 A. composition comprising the above materials in essentiall the proportions given, fires with approximately the same current consumption, and hence at approximately the same temperature as a mixture of eighty parts of mercury fulminate and twenty parts of potassium chlorate. Such a composition may be used in any of the metallic shells employed in the industry, and is entirely compatible with either mercury fulminate or lead azide priming compositions. Furthermore, even after it has absorbed appreciable quantities of moisture, it will fire with a current consumption approximating that required by dried material, and in this moist condition it exerts no corrosive action on common alloys used for bridge wires. Also, the scnsitiveness of this ignition mixture, to both shock and friction, is lower than that of fulminate-chlorate mixtures, and for that reason it may be handled. and used with less hazard.

It will be understood, of course, that the new compositions comprising my invention may be arranged in the metallic shell in any suitable manner according to the practice in making electric blasting caps. For a diamenace In Figure 2, like characters represent the same elements as shown in Figure 1, except i designates the lead azide-lead styphnate compound in place of the 90-10 F. C. primer. I

As many apparently widely diflerent embodiments of this invention may be made without departing from the spirit thereof, it is to be understood that I do not limit myself to the foregoing examples or descriptions except as indicated in the following patent claims:

I claim:

1. An electric blasting cap comprising a metallic shell, a pressed detonating charge, a loose charge of ignition material consisting of a mixture of sulphocyanate, an oxidizing compound and a low ignition point fuel, and a bridge wire attached to current leading wires embedded in said loose charge.

2, An electric blasting cap comprising a metallic shell, a pressed charge of a secondary detonating compound, a pressed charge of a primary detonating compound, a loose charge of ignition material consisting of a mixture of sulphocyanate, an oxidizing compound and a low ignition point fuel, and a bridge wire attached to current leading wires embedded in said loose charge.

3. An electric blasting cap comprising a metallic shell, a pressed charge of a secondary detonating compound, a pressed charge of a primary detonating compound, a loose charge of ignition material consisting of a mixture of lead sulphocyanate, potassium chlorate and a low ignition point fuel, and a bridge wire attached to current leading wires embedded in said loose charge. I

4. An electric blasting cap comprising a metallic shell, a pressed charge of a secondary detonating compound, a pressed charge of a primary detonating compound, a loose charge of ignition material consisting of a mixture of lead sulphocyanate, potassium chlorate and a low ignition point nitric ester, and a bridge wire attached'to current leading wires embedded in said loose charge.

5. An electric blasting cap comprising a metallic shell, a pressed charge of a secondary detonating compound, a pressed charge of a primary detonating compound, a loose charge of ignition material consisting of a mixture .of lead sulphocyanate, potassium chlorate and ground pyro powder, and a bridge wire attached to current leading wires embedded in said loose charge.

6. An electric blasting cap comprising a metallic shell, a pressed charge of a secondary detonating compound, a pressed charge of a primary detonating compound, a loose charge of ignition material consisting of a mixture of from 3050% lead sulphocyanate, 1030% potassium chlorate and 3050% ground pyro powder, and a bridge wire attached to current leading wires embedded in said loose charge.

7 An electric blasting cap comprising a metallic shell, a pressed base charge of tetranitromethylaniline, a pressed priming charge of lead azide together with an ignition and binding material either mixed with or superimposed upon said lead azide, a loose ignition charge consisting of a sulphocyanate, an oxidizing compound and a low ignition point fuel, and a bridged wire attached to current leading Wires embedded in said loose charge.

8. An electric blasting cap comprising a metallic shell, a pressed base charge of tetranitromethylaniline, a pressed priming charge of lead azide together with an ignition and binding material either mixed with or superimposed upon said lead azide, a loose ignition charge consisting of lead sulphocyanate, potassium chlorate, and ground pyro powder, and a bridge wire attached to current leading wires embedded in said loose charge.

In testimony whereof, I affix my signature.

HAROLD A. LEWIS. 

